This invention relates to the use of titanium aluminide materials, and, more particularly, to the protection of such materials against high temperature, oxidative environments.
Titanium aluminides are a class of intermetallic compounds based upon alloys of titanium, aluminum, and other elements. Two titanium aluminides of particular interest are gamma titanium aluminide and alpha-2 titanium aluminide. These materials a re of relatively low density as compared to nickel-based alloys, being based upon the light element s titanium and aluminum, and of excellent specific modulus and strength at intermediate temperatures.
The titanium aluminides have properties intermediate those of metals and ceramics. They exhibit good elevated temperature properties characteristic of ceramics, but also have some degree of ductility characteristic of metals. This ductility is important in most engineering applications, inasmuch as the ductility can impart fracture toughness, resistance to crack propagation, and resistance to thermal shock. The titanium aluminides also have coefficients of thermal expansion that are relatively low as compared with most metallic structural materials, which also contributes to reduced susceptibility to thermal shock damage.
Titanium aluminides are candidates for use in aircraft gas turbine jet engines, in such parts as exhaust structures, high pressure compressor blades and disks, inlet guide vanes, combustor cases, and possibly low pressure turbine blades. In these applications, the titanium aluminides would be subject to intermediate temperatures, and simultaneously to environmental attack in the form of oxidation, hot corrosion, hot salt stress corrosion cracking, and interstitial embrittlement. Titanium is a moderately reactive metal, and the titanium aluminides tend to be susceptible to environmental damage.
Although the titanium aluminides offer excellent potential for use in moderate-temperature structural applications, there is a need for an approach to protecting these materials against thermally and environmentally induced damage. The present invention aids in overcoming such shortcomings.